Optocouplers are often used to provide galvanic isolation between different voltage sources in an electronic circuit. Functions of optocouplers include providing high voltage package isolation and isolating noise of a main signal from a resulting signal. In an electronic circuit, an optocoupler ensures electric isolation. For example, optocouplers are used in applications such as telecommunications equipment, programmable controllers, direct current (DC) to DC converters, switch-mode power supplies, alternating current (AC) to DC converters and battery chargers. Optocouplers are disclosed and discussed in Vishay Telefunken, “General Description Basic Function”; Vishay “Optoelectronics”; Mikami et al., U.S. Pat. No. 4,614,958; Brown, U.S. Pat. No. 5,150,438; and Gempe et al., U.S. Pat. No. 6,013,251, the disclosures of each of which are hereby incorporated herein by reference.
An optocoupler may be considered comparable to a transformer or relay in some cases. However, optocouplers are typically smaller, ensure considerably shorter switching times, eliminate contact bounce, eliminate interference caused by arcs, and do not experience mechanical wear. Thus, optocouplers are particularly well suited for circuits used in microelectronics and also in data processing and telecommunication systems. Optocouplers are also used to promote component safety, such as in switch-mode power supplies.
In practice, a control circuit or the like is typically located on one side of the optocoupler, for example the emitter side, while a load circuit is located on the other side, the detector side in this example. The circuits are electrically isolated from each other by the optocoupler. Signals from the control circuit are transmitted optically to the load circuit, and are therefore free of reciprocal effects.
In most cases, optical transmission by an optocoupler employs light beams with wavelengths spanning from the red to infrared range. The bandwidth of signals transmitted by an optocoupler typically range from a DC voltage signal to frequencies in the MHz band, although signal frequencies in the GHz range are possible.
FIG. 1 shows an optocoupler configuration representative of the majority of optocoupler packages found today. As shown in FIG. 1 optocoupler package 100 defines light emitting device or diode (LED) 102 directly above detector 104 separated by generally transparent insulating material 109. Also shown in FIG. 1 for completeness are lead 103 coupled to LED 102 and lead 106 coupled to detector 104 by bond wire 105. Leads 103 and 106 provide signal communication between components of optocoupler package 100 and those external thereto.
In the above conventional configurations, the package height is limited by at least the sum of the device heights (height of LED 102 plus the height of detector 104), with additional material such as transparent insulating material 109 and mold compound 107 required to complete the package adding to the package height. However, as today's electronic applications become more and more complex and integrated, there is a continuing need to reduce component package size and capacity without sacrificing functionality. This becomes more challenging with the emergence of notebook computers, personal digital assistants (PDA), cellular telephones, and the like.
FIG. 2 shows an optocoupler package configuration representative of those described in U.S. Pat. Nos. 5,150,438 and 6,031,251, referenced above. Specifically, shown in FIG. 2 is an in-line or coplanar arrangement for a wide body optocoupler package 200, providing a reduced optocoupler profile or height (although this configuration may have a larger substrate footprint than optocoupler package 100). Such coplanar optocoupler packages typically employs a transparent insulation material 209, such as silicone, surrounding LED 202 and detector 204. Further, a reflective material 211, such as a white coating may coat transparent material 209. Mold compound 207 encapsulates the components of optocoupler package 200. Also shown in FIG. 2 are lead 203 coupled to LED 202 and lead 206 coupled to detector 204 by bond wire 205. Leads 203 and 206 provide signal communication between components of optocoupler package 200 and those external thereto, such as devices disposed upon printed circuit board 201.
Typical processes of creating both the clear insulation 209 and reflective layer 211 are cumbersome, slow and expensive, as the entire clear silicone insulate must be enclosed to restrict the LED light from escaping into mold compound 207. The shape of the optocoupler's profile, especially the clear silicone insulate, is crucial to performance, as this affects the light coupling efficiency of the optocoupler. However, typical methods of dispensing or depositing the silicone do not produce an accurate reproducible shape. With this process limitation, limits the number of optocouplers that may be integrated within a package, rendering the production of multichannel optocouplers problematic. Additionally, in the above linear configurations, indirect or reflective light coupling also results in inefficiencies in the reflection of the light.
Prior attempts to address these issues have had unsatisfactory results. For example, prior attempts have be made to increase the output of a white coating by increasing a matrix design of the leadframe. Other prior attempts to maximize output have called for use of a spray painting processes to apply the white reflective layer. While these methods have, to some degree, improve the output of devices and reduced cost, other problems have resulted. For example, a complicated leadframe matrix results in a inconsistent disposition of the reflective coating and a spray paint process often produces inconsistent coverage, which degrades the high voltage performance of an optocoupler.